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# A multi-armed bandit implementation inspired by
# @aaronsw and victorykit/whiplash
require 'simple-random'
module Split
module Algorithms
module Whiplash
class << self
def choose_alternative(experiment)
experiment[best_guess(experiment.alternatives)]
end
private
def arm_guess(participants, completions)
a = [participants, 0].max
b = [participants-completions, 0].max
s = SimpleRandom.new; s.set_seed; s.beta(a+fairness_constant, b+fairness_constant)
end
def best_guess(alternatives)
guesses = {}
alternatives.each do |alternative|
guesses[alternative.name] = arm_guess(alternative.participant_count, alternative.all_completed_count)
end
gmax = guesses.values.max
best = guesses.keys.select { |name| guesses[name] == gmax }
best.sample
end
def fairness_constant
7
end
end
end
end
end
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